The operational lifetime of an integrated circuit (a “chip”) is directly related to the operating temperature of the chip. Should any portion of the chip reach an over-temperature condition (where the portion of the chip exceeds a known temperature limit which may be as high as a temperature above which the chip will be irreversibly damaged), that portion the chip might fail for a variety of reasons, such as electromigration-induced failure of metal conductors on the chip. To protect the chip from overheating, a thermal protection circuit may be provided that disables or shuts down various circuits on the chip to reduce power consumption thereof. The thermal protection circuit is triggered when the temperature of the chip exceeds a trip-point temperature. Generally, the trip-point temperature is less than the known temperature limit which is less than the irreversible damage temperature.
A typical thermal protection circuit comprises an on-chip temperature sensor. But because the on-chip temperature sensor is typically much smaller than the chip as a whole, the temperature sensor might be located in an area of the chip that is colder than other areas of the chip. This could lead to premature chip failure notwithstanding the use of a thermal protection circuit. For example, even though a thermal protection circuit that has a trip-point temperature equal to the known temperature limit but does not detect an over-temperature condition, because the temperature sensor could be in a “cold” part of the chip, there might be portions of the chip significantly hotter than the known temperature limit and the life of the chip is thereby shortened.
Because of the uncertainty of where and what the highest temperature is on the chip at any given time, the trip-point temperature value is set significantly lower than the known temperature limit. To guarantee that no portion of the chip, regardless of where and how it is used, exceeds the known temperature limit, the trip-point temperature is typically set so low that the chip will shut down well before any part of the chip reaches the known temperature limit, effectively reducing the operating temperature range of the chip.